The University of Colorado at Boulder, in collaboration with University of California at Davis, Scientific Aviation, and the National Institute of Standards and Technology (NIST) will quantify emissions from natural gas storage facilities and provide an emissions estimate suitable for the Environmental Protection Agency’s (EPA's) Greenhouse Gas Inventory (GHGI). The measurements collected to inform emission estimates include ground-based regional-scale measurements at a variety of storage facilities for extended periods (continuous measurements over multiple months) each using a unique laser technology with minute time resolution and sensitivity to leaks down to 0.1 kg hr-1, together with broad ranging aircraft measurements at those and additional facilities. The campaign will achieve 1) continuous capture of diurnal to seasonal variability of emissions from entire facilities with component-level resolution (e.g. specific compressor, sealed well head, etc. emissions rates), 2) complementary and wide-spread aircraft surveys to assess and characterize the mean seasonal total emissions rates of many different facilities, and 3) combination of the detailed ground based and aircraft measurement data with Large Eddy Simulation transport models for determining emission inventories and reducing uncertainties. The integration of these independent yet highly complementary datasets will provide, for the first time, quantification of the mean state and temporal variability (diurnal to annual) of emissions from natural gas storage.
University of Colorado, Boulder, CO 80309
University of California, Davis, CA 95616
Scientific Aviation, Boulder, CO 80301
National Institute of Standards and Technology, Boulder, CO 80305; Gaithersburg, MD 20899
Very few research studies have concentrated specifically on quantifying methane emissions from underground natural gas storage wells and fields, which can involve complex infrastructure spread over hundreds or thousands of acres (5-10 square miles). The vast underground gas reservoirs may be connected to dozens of surface access points, for example old well heads in the case of a depleted reservoir field. Each is capable of leaking methane, as are the arrangements of handling equipment and compressor stations located on site. The EPA’s GHGI includes an estimate for underground natural gas storage, but that estimate is limited in scope and based on emissions from compressors. Amidst a climate of increasing scientific and public interest in quantifying the amount of methane lost to the atmosphere along the natural gas supply chain, the storage sector has quickly become recognized as a critically under-studied component. In addition, new state and federal safety regulations for the storage sector are already in process following the recent Aliso Canyon blowout event. An understanding of emissions from this sector will be critical for informed policymaking.
The project provides a highly cost-effective method for quantifying the entire cross-industry spectrum of underground natural gas storage wells and fields. From a scientific standpoint, this research fills an important gap in knowledge of the midstream natural gas supply chain – the storage sector. The comprehensive nature of the study, covering all important aspects of emissions quantification (total emissions across many fields, time history and variability, and uncertainty analysis), will create a complete emissions inventory for the sector. Furthermore, the project will have long-term benefits for the environmental impacts of the natural gas storage system by providing important information about leak rates and frequencies, and specific high-risk components in use in the storage sector to operators and policymakers. Finally, this approach is a more cost and resource efficient means to quantify methane emissions from underground storage facilities than is currently available, and may represent a new paradigm for emissions studies in other sectors with regional footprints.
The aircraft team has begun measurement of emissions from other underground natural gas storage sites across the US (including Alaska), ahead of schedule.
The ground-based dual-comb spectrometer was successfully deployed at the first storage site.
The team has demonstrated collection of data from the first storage facility with 100% remote operation.
The inversion/modeling team has performed inversions using data collected from the first storage site concurrent with aircraft mass-balance estimates from the same site. Closure between methods has been achieved during the first simultaneous measurements using the air and ground platforms.
The team demonstrated the acquisition of time-resolved aircraft- and ground-based data from the first storage site. The team provided time-resolved methane emissions estimates using ground-based and aircraft measurements, which demonstrated the successful integration of all components of the observing network (ground, aircraft, modeling/inversions) at the first storage site.
The ground-based dual-comb spectrometer is complete, and underwent testing at the Table Mountain Test Site 8 km north of Boulder, CO.
The preparation and development of the micrometeorological instrument package, as well as preparation of a low-rate (~1 Hz) horizontal wind speed measurement instrument that can be used to infer micrometeorological parameters, has been completed. The installation team continues to await FAA approval for installation on the aircraft. In the meantime, the team has developed an alternate method of calculating surface heat fluxes (and thus convective velocity scales) by similar relationships.
The ground- and aircraft-based emissions measurement systems have been successfully deployed at the first storage site. The measurement campaign using both platforms is underway and is continuing to gather information about emissions from the first storage site. Modeling efforts to obtain emissions estimates have been completed and continue along-side data acquisition. Implementation of inversion efforts using new technical developments for atmospheric dispersion modeling (the combination of Lagrangian particle dispersion modeling with Large Eddy Simulation flow fields) are underway, and comparisons with results obtained using simpler modeling techniques are forthcoming. The team plans to continue both ground- and aircraft-based measurement campaigns into the winter months.
Additional aircraft measurements have been made at sites across the US. States in which measurements have been made now include: Illinois, Alaska, Michigan, Pennsylvania, and Kentucky. As regular flights continue at the first storage site where the ground system is deployed, there will be an expansion of the measurement database to storage fields in other states and of other sizes and reservoir characteristics. Efforts are ongoing to obtain the geospatial information necessary to potentially undertake new flights in states such as Texas, Oklahoma, Missouri, Louisiana, and elsewhere.